Information Technology Reference
In-Depth Information
a.
The user issues a command (for example, “get finalpaper.rtf”
asks the file server to send the file “finalpaper.rtf” to the user;
the statement “put finalpaper.rtf” asks the local machine to
send the file to the file server).
b.
The client machine and file server respond with the infor
mation requested.
6.
When the user has moved the desired files, the user issues the
command “quit” to end the interaction.
Altogether, FTP transfers one or more complete files between a
local computer and a file server. By accessing an FTP site, for exam
ple, Steve could successfully retrieve the version of the paper made
available by Karen or Ella, as illustrated in Figure 9.2. After he has
edited it, he would want to upload his latest version of their work.
When the goal is to update a file stored on a server, the process en
tails three basic steps:
1.
Use FTP to copy the file from the server to the user's local
computer.
2.
Use the local computer to revise the copy of the file stored lo
cally.
3.
Use FTP to copy the new version of the file back to the file
server—often overwriting the old copy stored there previously.
In technical terms, FTP is a simple example of a
client/server
model of computing. The
server
provides a service or resource in re
sponse to requests by a
client
. In our groupproject example, Steve's
computer would be the client, requesting the common file server to
allow him to download the latest version of the file. The FTP frame
work provides a careful specification for a limited range of client re
quests, and the server responses are similarly limited and precisely
defined.
Remote File Access: The other common approach for accessing
files involves a
remote-service mechanism
that allows an ongoing in
teraction between a client (the user) and the file server. In the case
of editing a file, the user may want to view various parts of a file,
delete sections, make additions at any point in the file, or revise por
tions. Ella, for example, may want to add more to one of Karen's in
troductory paragraphs or edit their paper's conclusions. From Ella's
